1. Field of Invention
This invention relates to a high efficiency, broad beam lighting device which employs as a light source a plurality of LED lamps disposed within a hollow of a converging lens. Each LED lamp emitting light concentrated by the converging lens to form an elongated light beam whereby the elongated light beams overlap such that the light at a central zone of one elongated light beam is bolstered by light extending into that central zone from an adjacent elongated light beam to form a composite elongated light beam having a specification azimuth and specification broad vertical beam spread.
2. Prior Art
Prior art developed designs which either maximized the intensity directly in front of each LED lamps of a plurality of LED lamps in the horizontal direction or minimized the divergence of the composite light beam about the horizontal. These two objectives are very similar but due to the fact that the converging lens is formed about a curved focal line in place of a focal point they are not always exactly the same. Although prior art designs sought to minimize the divergence of the emitted light about the horizontal, the final product would always have some small or minimal divergence or vertical beam spread due to the size of the light source, lens, contour, tolerances, etc. A primary component of prior art designs included locating the LED element exactly on or just slightly in front of the focal circle towards the lens. In the current invention the LED element is disposed closer to the lens than prior art in order to broaden the beam spread and increase the efficiency.
There are a variety of specifications which could apply to the lighting device of the current invention. Typically, one of these specifications would require a peak intensity at the center of the light beam and define the vertical beam angle as the angle between the vertical angular deviations from the center at which the peak intensity decreases to a percentage of the peak intensity. The decrease in intensity can have a number of values normally ranging from fifty to ninety percent. A similar technique is employed to establish the horizontal beam angle or beam spread. Other specifications do not require a central peak intensity but define the vertical and horizontal beam angles at the respective angular deviations from the center at which the intensity falls below a minimum value. A lighting device which emits a light beam having a central zone of depressed intensity is usually not desirable for many applications. In addition it can easily fail to meet specifications that require a centrally located peak intensity.
Some specifications require that the output beam comprise minimizing the vertical divergence exactly as designed by prior art. However, other specifications establish intensity requirements within a broad vertical beam spread throughout an azimuth. These other specifications are the subject of the current invention which increases the efficiency of lighting devices required to comply with specifications requiring light distributed within a broad vertical beam spread. The increase in efficiency in the current invention results from changes in the construction of the lighting device which would not be acceptable when the lighting device was required to meet the prior art objective of minimizing the vertical beam spread. Changes in construction between prior art and the current invention include changing from a relatively large to a relatively small focal length, changing the disposition of the apparent point of emission of each LED, employing flat ceramic LEDs devoid of lenses and mounting the ceramic LED lamps on the peripheral edge of the printed circuit board. Specifically, regarding the disposition of the LEDs, each LED is disposed with its point of emission closer to the lens than prior art. This current application LED placement always increases the divergence of the emitted light beam about the horizontal plane relative to the minimal divergence desired by a prior art and usually—but not always—creates a projected light beam having a central zone of low intensity relative to a surrounding peripheral zone. This change in the prior art design results in an emerging beam pattern of light concentrated by lens 1 emitted by each LED which would appear to be problematic for many applications. However, it is especially problematic for specifications which require a peak intensity at the center of the projected beam.
Prior art designs, as well as the current invention, include the goal of having a composite light beam which is uniform throughout a required azimuth. This objective is universal because lighting devices which emit non-uniform light beams require excessive power. Excessive power is consumed because the overall intensity of the emitted beam must be increased in order for all zones of the light beam to meet the minimum intensity requirements. Therefore, changes in prior art designs which could encourage azimuthal variations in the intensity of the emerging beam would normally be considered as problematic. Conversely, changes in prior art which would improve the azimuthal uniformity of the emerging light beam would be beneficial. Adding more LED lamps to a light of limited size would be beneficial. It is noteworthy to realize that the problem of maintaining a uniform intensity for each angle of a vertical beam spread throughout an azimuth intensifies as the vertical beam spread is increased from minimum to broad.
Typical prior art for a lighting device emitting light having a large azimuthal and small vertical beam spread can be found in U.S. Pat. No. 5,224,733 issued to Arimura in which a circular array of a large number of LED lamps direct their light into a linear fresnel lens to create a horizontal light beam throughout the azimuth. Arimura in Column 5, Lines 49-55 describes a focal circle having a one-inch diameter and eighty LEDs arranged in an array. This array is encircled by a thin linear fresnel lens. The use of LED lamps with optics tends to create dark zones in the output beam between LED lamps. The large quantity of LED lamps in his array helps to mitigate the potential problem of dark zones within the output beam between LED lamps.
Prior art implies using a large focal length relative to the size or outside diameter of the lens. Prior art additionally discloses problems relating to the shape of the LED lamp that is used. In McDermott U.S. Pat. No. 5,899,557 Column 10, Lines 57-59, he discloses the objective of increasing distance D2. This is equivalent to increasing the focal length. In his abstract, McDermott disclosed employing a plurality of LED lamps encircled by a curved cylindrical surface to concentrate the emitted light into a composite beam with the intensity of the projected beam maximized. McDermott in the referenced patent did not require the lens hollow employed in the current invention. In Column 12, Lines 7-15 McDermott disclosed moving his LED element relative to the focal point to change the vertical beam spread. This disclosed movement and its result was based upon analysis of a lens devoid of a hollow. The optics change with the addition of a hollow. McDermott did not reveal the central zone of reduced intensity that would result if the movement of the LED towards the lens of that patent continued or what significance that central depressed intensity zone would have.
In a second U.S. Pat. No. 6,048,083 also issued to McDermott, he employs classical lenses having a hollow to concentrate the light from his array of LED lamps. In this patent, McDermott places the apparent focal point of his LED lamps between the bent focal line and the interior wall of the lens in order to maximize the efficiency when concentrating light towards the horizontal to achieve minimal divergence. In Column 5, Lines 23-25 McDermott locates each LED element a slight distance on the lens side of the focal point. In Column 14, Lines 57-60 McDermott states his objective “to minimize divergence of light from said respective light emitting diode element about said horizontal plane”. Although not used in his prior art patent, in the current invention the term “minimum divergence curved line” is used to describe the location of the apparent points of emission of the LEDs in the McDermott prior art patent. This term simplifies the discussion in the current specification.
In addition, McDermott in FIG. 10, Column 13, Lines 34-66 discloses an apparent focal point problem with the T1 ¾ LED lens top lamps that can cause the lighting device to squander light. Specifically, the body of the T1 ¾ LED normally has a lens that refracts emitted light. This refraction creates a plurality of apparent focal points which causes the LED to appear to the lens as an enlarged light source. McDermott offers a spherical top LED as a preferred way to alleviate this problem. The spherical LED, theoretically, does not refract light emitted from the LED element and therefore, theoretically, does not cause the small LED emitter to appear large. This concept does minimize enlargement of the LED source but—due to manufacturing variations in the spherical contour and placement of the LED element—does not totally eliminate it. Nevertheless, this type of problem is one reason that prior art places its LED arrays at a substantial focal distance (visually observed from the figures provided in the referenced prior art) from the lens. If as indicated in the referenced prior art the objective is to minimize the divergence of the composite emitted light beam about the horizontal, then a small or minimum vertical beam spread is the goal. In order to maximize the light directed into a small vertical beam spread prior art designed to maximize control of the light. This was necessary as a slight misdirection would cause the light to miss its small target of a small vertical beam spread. In general, in order to control the light more effectively, it is desirable to have both a lens with a large focal distance combined with a very small or a point light source. The large focal distance indicated by prior art reduces misdirected light resulting from variations in light source placement or lens contour. It also reduces the negative consequences of enlargement of the light source related to shifting of the apparent point of emission. Since no light source is as small as a point source and since even small light sources can have apparent size enlargements due to refraction at their lens or body, it is usually desirable to have a large focal length to offset these problems. Unfortunately, the large focal length indicated by referenced prior art when combined with the plurality of LED emitters employed to assure an azimuthally uniform beam work against designing a lighting device which is compact, efficient and emitting light having a broad beam spread.
Finally, LED lamps with spherical domes can—due to their close disposition—have domes which intersect and divert diverging lights from adjacent LED lamps. A large focal length mitigates this problem.
Prior art encouraged a relatively large focal length because a large focal length—as previously described—solved many problems. A small focal length also had advantages which would have been known to prior art designers such as a reduction in both the mass of the converging lens and the ability to add additional LED lamps to a lighting device of limited size. However, when prior art considered the issue, the large focal length was the best choice. Two factors that were included when making that decision. The first was overcoming possible enlargement of the apparent point of emission resulting from the limited number of commercially available LED packages both bright enough to meet intensity requirements and devoid of domes or lenses. The second was the desire to have an emerging light beam of minimal divergence about the horizontal. In general, a shortened focal length will always increase the percentage of light that is misdirected because the LED placement varies and the LED element is not a point source. However, as the permissible vertical beam spread of the composite elongated light beam is broadened, the loss in efficiency due to a reduced focal length is reduced. The above factors in addition to the reduced mass of the lens resulting from a reduced focal length make it the preferred choice.
The current invention employs a short focal length to create a lighting device of improved efficiency and reduced size.
The referenced prior art teaches or at least implies the following concepts which are not taught in the current invention:                having a lens which defines a focal distance which is substantial in magnitude relative to the radius of the lens.        positioning the LED lamps at the focal point or at a slight distance from the focal point towards the lens on the minimum divergence curved line to minimize the horizontal divergence of the light as it emerges from the lens.        having a lighting device designed to minimize divergence of the light about the horizontal.        
The referenced prior art teaches the following concepts which are also employed in parts of the current invention:                a curved cylindrical surface or a fresnel lens which is formed to provide a curved focal line, bent focal line or a plurality of focal points to provide an emerging elongated light beam.        a curved array of LED lamps with each lamp having its apparent point of emission between its related focal point and the lens (see McDermott U.S. Pat. No. 6,048,083 Column 5, Lines 22-26). The current application disposes the apparent points of emission even closer to the lens.        
3. Objects and Advantages
The objects and advantages of the present invention are to create a high efficiency lighting device employing a converging lens to concentrate light from a plurality of LED lamps into an elongated composite light beam having a broad vertical beam spread and a uniform intensity throughout an azimuth.                to provide an LED lighting device which minimizes the operating temperature of its LED lamps to thereby increase their efficiency resulting in increased efficiency for the entire lighting device;        to maximize the percentage light energy emitted by a plurality of LED lamps which is concentrated into a specification broad vertical beam spread throughout a specified azimuth.        
In the current invention ceramic LED lamps are acceptably powerful and because they are devoid of a dome or lens they virtually eliminate enlargement and shifting of the apparent point of emission. Also, in the current invention the emerging light is no longer required to be concentrated with minimal divergence about the horizontal. In practice, many specifications do not require the light to be concentrated with minimal divergence about a plane but instead require the light to be concentrated within a broad vertical beam spread typically from four to fifty degrees. The elimination of the apparent shifting of the point of emission and the broad beam spread specifications individually and in combination make lighting devices constructed with a small focal length and the LED disposition further from the focal point and closer to the lens in accord with the current invention a superior design.
The referenced prior art does not teach or address the following concepts which are employed in the current invention:                employing the concepts of a small focal length, peripherally mounted LED lamps and placement of the apparent points of emission of each LED between the minimum divergence curved line and the lens to provide a compact and efficient lighting device capable of emitting a powerful elongated light beam having a broad vertical beam spread.        Maximizing the intensity and uniformity of an elongated light beam having a broad vertical beam spread from a lighting device of limited size by reducing the focal length of the converging cylindrical lens.        Increasing the quantity of LED lamps deployable within a lighting device of limited size by reducing the focal length thereby providing a larger diameter for the array of LED lamps resulting in increased uniformity in the emerging elongated light beam.        Disclosing the concept that the focal length can be reduced and efficiency increased for specifications which mandate broad vertical beam spreads.        Shaping the lens and positioning the plurality of LED lamps so that a central depressed intensity zone created by one LED is buttressed with light from at least one but possibly several adjacent LEDs.        Using ceramic LED lamps without lenses to virtually eliminate dome or lens related shifting of the point of light emission.        Employing a plurality of ceramic LED lamps each of which comprise a ceramic body capable of withstanding high heat attached to the peripheral edge of a printed circuit board to disperse that heat.        Soldering ceramic LED lamps devoid of wire leads to the peripheral edge of the printed circuit board to provide room on the top and the bottom surface of the printed circuit board for other components.        Improving the efficiency of lighting devices requiring a broad vertical or transverse beam spread by having separately or in combination: a lens with a short focal length, LED lamps positioned further from the focal point than the slight distance from the focal point disclosed by prior art (see McDermott U.S. Pat. No. 6,048,083 Column 5, Lines 22-26) and employing ceramic LED lamps devoid of a lens.        reducing the focal length to broaden the vertical beam spread of the elongation zone to assure it completely overlaps the adjacent central zone.        
Further objects and advantages are realized through combinations of the above distinct advantages.